The present invention relates to the processing of substrates. More particularly, the present invention relates to an improved method and apparatus for tuning a process recipe to target dopant concentrations in a doped layer formed over a semiconductor substrate. According to a specific embodiment, the present invention may be used to tune a borophosphosilicate glass (BPSG) recipe to target dopant concentrations in a deposited BPSG layer. Of course, the present invention may also be applied to the formation of other doped layers.
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a doped layer on a semiconductor substrate. A doped dielectric layer can be deposited by chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired film. Plasma-enhanced CVD (PECVD) processes promote excitation and/or disassociation of the reactant gases by the application of radio frequency (RF) energy to a reaction zone near the substrate surface, thereby creating a plasma to produce the desired film.
Semiconductor integrated circuits currently being manufactured follow ultra high density (e.g., about 0.5 to 0.35 micron) design rules, and circuits manufactured in the near future will follow even smaller design rules. As device sizes become smaller and integration density increases, issues which were not previously considered important by the industry are becoming of increasing concern. For example, consistently and reliably forming doped dielectric films, such as BPSG films, having specific target dopant concentrations is often important for applications requiring certain film properties that may be influenced by the dopant concentration levels.
In order to deposit doped films having specific target dopant concentrations in a consistent manner, the industry has traditionally resorted to the method of manually tuning the process recipe using a trial and error approach. First, initial process gas flow rates are set and a predetermined thickness of the desired doped film is deposited on a wafer. Then, the deposited doped film is tested to determine the dopant concentration levels resulting from deposition using the initial process gas flow rates. If the measured dopant concentration levels are not the desired target dopant concentrations, the equipment support engineer adjusts the process gas flow rates based on her/his personal experience with the performance of this specific system in the previous trial deposition. After the predetermined thickness of the doped film is deposited on a wafer using the adjusted flow rates, the dopant concentration levels are measured again. Depending on the empirical results from prior trial depositions for this specific system, the equipment support engineer may repeatedly engage in this iterative, trial and error approach. This manual tuning procedure is often very rough and may take several hours before resulting in a somewhat more refined tuning.
The manual tuning process is labor intensive, complicated, and often very time consuming, taking at least several hours and often up to an entire day, before resulting in the targeted dopant concentration levels. Also, the total time to tune the process using the trial-and-error approach often depends on the skills and experience of the individual equipment support engineer. Excessive time spent on manually tuning the process translates to an inefficient use of process time for the customer or user of the deposition system. Further, it is often time consuming, inefficient, and difficult to train an equipment support engineer (or other person) to tune a process sufficiently well. Another difficulty is that the results of identical tuning procedures of the same process recipe may vary in different deposition systems depending on the individual deposition chamber in use. Therefore, the manual tuning process must be individualized to the extent possible for the deposition chamber used. In addition, the speed at which the process tuning may be completed depends on how close the initial process flow rates used are to the actual process flow rates required to reach the targeted dopant concentration levels. The initial process flow rates used to try to reach target dopant concentration levels are based on trend curves, which may deviate from the actual system behavior.
From the above, it can be seen that it is desirable to have a method and apparatus for forming doped films with targeted dopant concentrations in a consistent, reliable, and efficient manner without regard to either the individual chamber differences or the individual tuner's skills and experience level.